Consider subpixel accumulation when invalidating paint

Source/core/rendering/RenderLayerScrollableArea.cpp

 /*
  * Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011, 2012 Apple Inc. All rights reserved.
  *
  * Portions are Copyright (C) 1998 Netscape Communications Corporation.
  *
  * Other contributors:
  *   Robert O'Callahan <roc+@cs.cmu.edu>
  *   David Baron <dbaron@fas.harvard.edu>
  *   Christian Biesinger <cbiesinger@web.de>
  *   Randall Jesup <rjesup@wgate.com>
@@ skipping 383 matching lines @@
 
         if (usesCompositedScrolling() || onlyScrolledCompositedLayers)
             requiresRepaint = false;
     }
 
     // Just schedule a full repaint of our object.
     if (requiresRepaint) {
         if (box().frameView()->isInPerformLayout())
             box().setShouldDoFullPaintInvalidationAfterLayout(true);
         else
-            box().invalidatePaintUsingContainer(repaintContainer, pixelSnappedIntRect(layer()->renderer()->previousPaintInvalidationRect()), InvalidationScroll);
+            box().invalidatePaintUsingContainer(repaintContainer, layer()->renderer()->previousPaintInvalidationRect(), InvalidationScroll);
     }
 
     // Schedule the scroll DOM event.
     if (box().node())
         box().node()->document().enqueueScrollEventForNode(box().node());
 
     if (AXObjectCache* cache = box().document().existingAXObjectCache())
         cache->handleScrollPositionChanged(&box());
 
     InspectorInstrumentation::didScrollLayer(&box());
@@ skipping 1024 matching lines @@
     DisableCompositingQueryAsserts disabler;
     return layer()->hasCompositedLayerMapping() && layer()->compositedLayerMapping()->scrollingLayer();
 }
 
 bool RenderLayerScrollableArea::needsCompositedScrolling() const
 {
     return scrollsOverflow() && box().view()->compositor()->acceleratedCompositingForOverflowScrollEnabled();
 }
 
 } // Namespace WebCore